Over 99% of Spaniards speak Castilian Spanish, either as their primary or secondary language, making it the dominant and unifying language across Spain

. Another source notes that about 94% of the Spanish population speaks Castilian Spanish, highlighting its prevalence especially in northern and central Spain

. Spanish (Castilian) is the only official language nationwide and is spoken habitually and natively by the vast majority of the population, including in regions where other co-official languages exist

. Thus, nearly all Spaniards speak Castilian Spanish in some capacity.